The present invention relates to a process for producing a hydrogenated xcex1-olefin-dicyclopentadiene copolymer, a method for molding the same and an optical material obtained from the same.
Alpha-olefin-cyclic olefin copolymers obtained by the addition-copolymerization of an xcex1-olefin and a cyclic olefin are synthetic resins having excellent transparency, heat aresistance, weatherability, chemical resistance, solvent resistance, dielectric characteristics and various mechanical properties and are widely used in various fields.
These xcex1-olefin-cyclic olefin copolymers are generally produced by the addition-copolymerization of an xcex1-olefin and a cyclic olefin in a hydrocarbon-based solvent such as toluene, cyclohexane or hexane in the presence of an addition polymerization catalyst.
When a copolymer of an xcex1-olefin and a cyclic olefin having at least two double bonds between carbons, namely, a cyclic polyene, is used as a resin, the double bonds between carbons contained in the copolymer must be saturated by hydrogenation to improve heat resistance, weatherability and light resistance. The hydrogenation of a polymer is generally carried out through a reaction between a copolymer and hydrogen in the presence of a heterogeneous or homogeneous hydrogenation catalyst.
The inventors of the present invention have found that, among xcex1-olefin-cyclic polyene copolymers, an xcex1-olefin-dicyclopentadiene copolymer, which is obtained when dicyclopentadiene is used as a cyclic polyene, does not contain the linkages of the dicyclopentadiene and has high chemical homogeneity and that a hydrogenated xcex1-olefin-dicyclopentadiene copolymer is particularly excellent in optical homogeneity and transparency and suitable for use as an optical material for an optical disk substrate or the like and have previously proposed the copolymer (WO98/33830).
The hydrogenated xcex1-olefin-dicyclopentadiene copolymer is generally produced through the step of polymerizing an xcex1-olefin and dicyclopentadiene in a hydrocarbon solvent, the step of hydrogenating the obtained xcex1-olefin-dicyclopentadiene copolymer, the step of removing the catalyst and the step of removing volatile components.
In the polymerization reaction step, in order to obtain a copolymer having high chemical homogeneity, it is extremely important to maintain the ratio of the xcex1-olefin to the dicyclopentadiene at a value higher than a predetermined value. As a result, unreacted dicyclopentadiene inevitably remains in a solution after polymerization. In the subsequent hydrogenation reaction step, the residual dicyclopentadiene is hydrogenated together with the copolymer to be converted into tetrahydrodicyclopentadiene and eventually separated from the hydrogenated copolymer together with the solvent in the step of removing volatile components.
The ignition point of the by-produced tetrahydrodicyclopentadiene is 235xc2x0 C., which is much lower than that of a commonly used solvent (toluene: 480xc2x0 C., cyclohexane: 260xc2x0 C.). Therefore, it is not preferred from the viewpoint of preventing a danger to keep a polymer solution containing tetrahydrodicyclopentadiene at a temperature higher than 235xc2x0 C. in ordinary equipment, even if it is in an inert atmosphere. This problem can be solved by using perfect airtight equipment but a great load is imposed on equipment in an industrial-scale production. Therefore, it is very difficult to produce the hydrogenated xcex1-olefin-dicyclopentadiene copolymer on an industrial scale.
JP-A 64-54011, JP-A 5-17527 and JP-A 8-239415 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) disclose solvents used for a copolymerization reaction between an xcex1-olefin and dicyclopentadiene and JP-A 63-243103 discloses a solvent used for the hydrogenation reaction of an ethylene-dicyclopentadiene copolymer. Most of the solvents are compounds having a boiling point lower than the boiling point of tetrahydrodicyclopentadiene (194xc2x0 C. at 760 mmHg). When a solvent having such a low boiling point is used, the solvent is first distilled off in the step of removing volatile components and then tetrahydrodicyclopentadiene is distilled off. However, when the solvent is almost completely distilled off, the hydrogenated copolymer becomes solid at a temperature lower than the ignition point of tetrahydrodicyclopentadiene, thereby making it extremely difficult to completely distill off tetrahydrodicyclopentadiene. Some solvents having a boiling point higher than that of tetrahydrodicyclopentadiene are also enumerated. All of them, however, have a high melting point and are not suitable for use in a polymerization reaction or have a low ignition point of around 250xc2x0 C. or low solubility for polymers. Therefore, they cannot be used in actual production.
As described above, tetrahydrodicyclopentadiene cannot be removed from the copolymer solution safely and efficiently by conventionally known methods.
When a commonly used hydrocarbon-based solvent such as toluene or cyclohexane is used, there arises another serious problem to be solved in the step of removing volatile components. Since the boiling point of the hydrocarbon-based solvent is lower than the melting temperature of the polymer by 100xc2x0 C. or more, the polymer becomes solid when the solvent is completely distilled off, thereby making stirring extremely difficult. It is possible to obtain a molten polymer without passing through a solid state by carrying out the operation of removing volatile components in a pressurization system and increasing the boiling point of the solvent. However, the control of a reaction is extremely difficult and a great load is imposed on equipment. Thus, there has been no method for directly converting the polymer from a solution state into a molten state with ease, and the development of this method has been desired.
On the other hand, not only transparency but also various characteristic properties such as optical isotropy (low birefringence), dimensional stability, weatherability and thermal stability are required for plastics used as an optical material for optical disk substrates and optical lenses and the like. For these optical applications, polycarbonates and poly(methyl methacrylate) have been mainly used. However, molded products of polycarbonates are liable to show optical anisotropy due to large specific birefringence, whereas poly(methyl methacrylate) are inferior in dimensional stability due to extremely high water absorption and have low heat resistance. Although polycarbonates are mainly used for optical disk substrates nowadays, there arise concerns about such problems as the large birefringence of the polycarbonates and the warp of a disk by moisture absorption, along with a recent attempt to increase the capacity of a magneto-optical recording disk (MOD) or to increase the recording density as typified by the development of a digital video disk (DVD).
In view of the above situation, the development of cyclic olefin polymers as substitutes for polycarbonates is now under way intensively. These cyclic olefin-based resins are expected to be used as thermoplastic transparent resins having small birefringence and high heat resistance for an optical material for optical lenses and optical sheets in addition to optical disk substrates.
It is an object of the present invention to provide a process for producing a hydrogenated xcex1-olefin-dicyclopentadiene copolymer.
It is another object of the present invention to provide a process for producing a hydrogenated xcex1-olefin-dicyclopentadiene copolymer, which is capable of removing unreacted dicyclopentadiene or tetrahydrodicyclopentadiene, which is the hydrogenated product of dicyclopentadiene, safely and efficiently.
It is still another object of the present invention to provide a method for melt molding of a hydrogenated xcex1-olefin-dicyclopentadiene copolymer.
It is a further object of the present invention to provide a method for melt molding of a hydrogenated xcex1-olefin-dicyclopentadiene copolymer, which is suitable for producing an optical material that is rarely colored and free from a fish eye or silver streak and that has excellent transparency and moldability, such as an optical disk substrate, optical lens or optical sheet.
It is a still further object of the present invention to provide an optical material obtained by the melt molding method of the present invention.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention are attained by a process for producing a hydrogenated xcex1-olefin-dicyclopentadiene copolymer (may be referred to as xe2x80x9cthe first production process of the present inventionxe2x80x9d hereinafter) comprising:
(1) the step of addition-polymerization of an xcex1-olefin having 2 or more carbon atoms and dicyclopentadiene in a hydrocarbon solvent in the presence of a polymerization catalyst, and then removing the polymerization catalyst as required, to produce an xcex1-olefin-dicyclopentadiene copolymer solution containing unreacted dicyclopentadiene;
(2) the step of adding a hydrogenation catalyst to the copolymer solution produced in the step (1) to hydrogenate the unsaturated double bonds of the xcex1-olefin-dicyclopentadiene copolymer so as to produce a mixture containing a hydrogenated xcex1-olefin-dicyclopentadiene copolymer; and
(3) the step of distilling of tetrahydrodicyclopentadiene formed in the hydrogenation reaction of the step (2) from the mixture containing a hydrogenated xcex1-olefin-dicyclopentadiene copolymer produced in the previous step,
wherein at least one of the following operations (i), (ii) and (iii) is carried out to ensure that a high-boiling hydrocarbon solvent is existent in an amount of at least 10 parts by weight based on 100 parts by weight of the hydrogenated xcex1-olefin-dicyclopentadiene copolymer at the end of the step (3):
(i) use of a high-boiling hydrocarbon solvent as at least part of the hydrocarbon solvent of the step (1),
(ii) addition of a high-boiling hydrocarbon solvent in the step (2), and
(iii) addition of a high-boiling hydrocarbon solvent in the step (3); and the high-boiling hydrocarbon solvent contains at least a hydrocarbon solvent having a boiling point at normal pressure of 195 to 300xc2x0 C. and an ignition point of 260xc2x0 C. or more.
Secondly, the above objects and advantages of the present invention are attained by a process for producing a hydrogenated xcex1-olefin-dicyclopentadiene copolymer (may be referred to as xe2x80x9cthe second production process of the present inventionxe2x80x9d hereinafter) comprising:
(1xe2x80x2) the step of addition-polymerizing an xcex1-olefin having 2 or more carbon atoms and dicyclopentadiene in a hydrocarbon solvent in the presence of a polymerization catalyst, and then removing the polymerization catalyst as required, to produce an xcex1-olefin-dicyclopentadiene copolymer solution containing unreacted dicyclopentadiene;
(2xe2x80x2) the step of distilling off the unreacted dicyclopentadiene from the xcex1-olefin-dicyclopentadiene copolymer solution containing the unreacted dicyclopentadiene produced in the step (1xe2x80x2) to produce an xcex1-olefin-dicyclopentadiene copolymer solution containing substantially no dicyclopentadiene; and
(3xe2x80x2) adding a hydrogenation catalyst to the xcex1-olefin-dicyclopentadiene copolymer solution produced in the previous step to hydrogenate the unsaturated double bonds of the xcex1-olefin-dicyclopentadiene copolymer to produce a mixture containing a hydrogenated xcex1-olefin-dicyclopentadiene copolymer,
wherein at least one of the following operations (ixe2x80x2) and (iixe2x80x2) is carried out to ensure that a high-boiling hydrocarbon solvent is existent in an amount of at least 10 parts by weight based on 100 parts by weight of the xcex1-olefin-dicyclopentadiene copolymer at the end of the above step (2xe2x80x2):
(ixe2x80x2) use of a high-boiling hydrocarbon solvent as at least part of the hydrocarbon solvent of step (1xe2x80x2), and
(iixe2x80x2) addition of a high-boiling hydrocarbon solvent in step (2xe2x80x2); and the high-boiling hydrocarbon solvent contains at least a hydrocarbon solvent having a boiling point at normal pressure of 195 to 300xc2x0 C. and an ignition point of 260xc2x0 C. or more.
The melt molding method and the optical material of the present invention will be described later.